This invention relates to an ethylene-propylene copolymer based resin composition which is good in moldability and provides molded articles high in both rigidity and impact resistance. The resin composition is suitable for molding into automobile bumbers.
In the current automobiles the bumper material has been changed from steel to synthetic resins such as polyurethane based resins or polypropylene based resins. The main objects of using resin bumpers are reducing the weight, preventing rusting and augmenting the freedom of design.
However, automobile bumpers formed of conventional resins are generally insufficient in rigidity and hence need to be reinforced by inserting metal reinforcements. Meanwhile, the current automobiles tend to become larger in body size to satisfy the requirements for higher performance and consequently become heavier in gross weight, whereas still there is a strong demand for further improvements in fuel economy. Therefore, it is advantageous to reduce the weight of various parts of automobiles, including bumpers, without sacrificing the performance.
Resin bumpers for automobiles are required to be high in both ridigity and impact resistance even at considerably low temperatures. Recently there are several proposals of polypropylene based resin compositions which are fairly high in the impact resistnce of the molded products such as automobile bumpers, as disclosed in JP 57-55952 A, JP 58-111846 A and JP 59-98157 A. However, bumpers formed of any of these resin compositions are insufficient in rigidity for restricting the amount of deformation in case of a collision and hence need to be reinforced by the insertion of metal reinforcements.